1. Field of the Invention
The present invention relates to a work vehicle and a work vehicle control method.
2. Background Information
A work vehicle drives a work implement and performs desired work. For example, the work implement of a hydraulic excavator has an arm, a boom, and a bucket. The arm, the boom, and the bucket are each driven by a hydraulic cylinder. By supplying hydraulic oil to each of the cylinders, the respective cylinders drive the arm, the boom, and the bucket. In detail, switching valves are connected with each of the cylinders and the supply direction of the hydraulic oil to each of the cylinders is switched by each of the switching valves. Due to this, the respective cylinders expand and contract to drive the arm, the boom, and the bucket.
Each of the switching valves is driven using a pilot pressure that is controlled according to a pilot pressure control valve. Here, the pilot pressure control valve controls the pilot pressure that depends on an operation amount of an operation lever. An electromagnetic proportional valve is installed between the pilot pressure control valve and each pilot port in each of the switching valves. Then, automatic control of each of the cylinders is possible by the control section controlling the electromagnetic proportional valve on the basis of the pilot pressure that is applied from the pilot pressure control valve (refer to Japanese Unexamined Patent Application Publication No. H9-105152). For example, the electromagnetic proportional valve is opened and closed by the control section controlling a current value of a current that is output to the electromagnetic proportional valve and it is possible to automatically control each of the cylinders as a result. Here, automatic control is a concept that also encompasses automatic control that includes work by an operator as a portion of the automatic control.
By automatically controlling each of the cylinders as described above, it is possible to automatically control the work implement. However, in a case where a configuration is adopted such that the electromagnetic proportional valve is installed between the pilot pressure control valve and each of the pilot ports of each of the switching valves and the control section controls the electromagnetic proportional valve on the basis of the pilot pressure that is applied from the pilot pressure control valve, there is a concern that the work implement will not be appropriately automatically controlled when the pilot pressure changes due to operation of the operation lever. For example, when control is executed in the hydraulic excavator to move a cutting edge of the bucket along a designed surface, the boom moves upward more than necessary when the operation amount of the operation lever increases and there are times when the cutting surface moves above the designed surface.
The present invention provides a work vehicle that is able to appropriately automatically control a work implement.
A work vehicle according to a first aspect of the present invention is provided with a work implement, a switching valve, an operation member, a pilot pressure control valve, an electromagnetic proportional valve, an upstream pilot flow path, a pressure sensor, and a control section. The switching valve is configured to switch a supply direction of a first hydraulic fluid which is supplied to the work implement. The operation member is configured to operate the work implement. The pilot pressure control valve is configured to control pressure of a second hydraulic fluid that drives the switching valve according to an operation amount of the operation member. The electromagnetic proportional valve is installed between the switching valve and the pilot pressure control valve. The upstream pilot flow path connects the pilot pressure control valve and the electromagnetic proportional valve. The pressure sensor is configured to detect pressure of the second hydraulic fluid inside the upstream pilot flow path. The control section selects at least one item of current value information from a plurality of items of current value information on the basis of the pressure that is detected by the pressure sensor. The control section is configured to set a current value of a current that is output to the electromagnetic proportional valve on the basis of the current value information that is selected. The current value information expresses a correspondence relationship between the current value of the current that is output to the electromagnetic proportional valve and the pressure of the second hydraulic fluid that is output from the electromagnetic proportional valve.
According to this configuration, the control section selects at least one item of current value information from the plurality of items of current value information on the basis of the pressure that is detected by the pressure sensor. Then, the control section sets the current value of the current that is output to the electromagnetic proportional valve on the basis of the current value information which is selected. As a result, the electromagnetic proportional valve is driven using a current with a more appropriate current value. As a result, a more appropriate pilot pressure is applied to the switching valve and the work implement is appropriately automatically controlled.
Typically, the pressure of the hydraulic fluid that is input into the electromagnetic proportional valve (the input pressure) and the pressure of the hydraulic fluid that is output from the electromagnetic proportional valve (the output pressure) are not limited to being equal. In detail, when the input pressure is different, there are cases where the output pressure is different even when a current with the same current value is output to the electromagnetic proportional valve. The control section estimates the operation speed of the work implement according to the input pressure. As a result, in a case where, for example, the input pressure is higher than the output pressure, the operation speed of the work implement that is estimated by the control section is faster than the actual operation speed of the work implement.
The following phenomena occur due to the above phenomena in a case of performing work where terrain is leveled along a designed surface using a hydraulic excavator. The operator performs an excavation operation with the arm and performs a lowering operation of the boom such that the cutting edge of the bucket moves along the designed surface. Here, the control section performs control, which raises the boom when it is determined that there is a high possibility that the cutting edge will be moved below the designed surface. When the operation speed of the arm, which is estimated by the control section, is faster than the actual operation speed of the arm, a phenomenon occurs where the control section moves the boom upward more than necessary and the cutting edge moves above the designed surface. This phenomenon is particularly likely to occur due to, for example, the pilot pressure increasing when an arm operation lever is further tilted to increase the speed of the work.
The control section according to the present invention sets the current value of the current that is output to the electromagnetic proportional valve on the basis of the appropriate current value information that corresponds to the input pressure as described above. As a result, it is possible for, for example, the pressure of the second hydraulic fluid that is input into the electromagnetic proportional valve and the pressure of the second hydraulic fluid that is output from the electromagnetic proportional valve to be substantially equal. As a result, the operation speed of the work implement, which is estimated by the control section, and the actual operation speed of the work implement are substantially equal. Accordingly, it is possible for the work vehicle according to the present invention to appropriately automatically control the work implement.
It is preferable that the control section be configured to set the current value that is output to the electromagnetic proportional valve on the basis of the at least one item of current value information that is selected such that the pressure of the second hydraulic fluid that is output from the electromagnetic proportional valve is equal to the pressure that is detected by the pressure sensor.
It is preferable that the plurality of items of current value information be items of information that are set for each of a plurality of specific pressures that are input into the electromagnetic proportional valve. The control section selects at least one item of current value information on the specific pressures, which are close to the pressure that is detected by the pressure sensor, from the plurality of items of current value information. The control section sets the current value of the current that is output to the electromagnetic proportional valve on the basis of the at least one item of current value information that is selected.
It is preferable that the control section be configured to select a first item of current value information from the plurality of items of current value information when the pressure that is detected by the pressure sensor is a first pressure. In addition, the control section is configured to select a second item of current value information from the plurality of items of current value information when the pressure that is detected by the pressure sensor is a second pressure. The control section sets the current value of the current that is output to the electromagnetic proportional valve using interpolation when the pressure that is detected by the pressure sensor is between the first pressure and the second pressure.
It is preferable that the control section set the current value of the current that is output to the electromagnetic proportional valve using linear interpolation when the pressure that is detected by the pressure sensor is between the first pressure and the second pressure.
It is preferable that the control section select the first and second items of current value information from the plurality of items of current value information when the pressure that is detected by the pressure sensor is between the first pressure and the second pressure. Then, the control section sets the current value of the current that is output to the electromagnetic proportional valve using interpolation of the current value that is set based on the first item of current value information and the current value that is set based on the second item of current value information.
It is preferable that the work implement have a cylinder that is driven by the first hydraulic fluid. The switching valve is configured to switch the supply direction of the first hydraulic fluid that is supplied to the cylinder.
It is preferable that the work implement be further provided with a vehicle body. The work implement has a boom, an arm, a boom cylinder, and an arm cylinder. The boom is attached to the vehicle body to be able to rotate. The arm is attached to the boom to be able to rotate. The boom cylinder is configured to drive the boom. The arm cylinder is configured to drive the arm. The switching valve is configured to switch the supply direction of the first hydraulic fluid that is supplied to the arm cylinder.
A work vehicle according to a second aspect of the present invention is provided with a work implement, a switching valve, an operation member, a pilot pressure control valve, an electromagnetic proportional valve, an upstream pilot flow path, a pressure sensor, and a control section. The switching valve is configured to switch a supply direction of a first hydraulic fluid that is supplied to the work implement. The operation member is configured to operate the work implement. The pilot pressure control valve is configured to control pressure of a second hydraulic fluid that drives the switching valve according to an operation amount of the operation member. The electromagnetic proportional valve is installed between the switching valve and the pilot pressure control valve. The upstream pilot flow path connects the pilot pressure control valve and the electromagnetic proportional valve. The pressure sensor is configured to detect pressure of the second hydraulic fluid inside the upstream pilot flow path. The control section selects at least one item of current value information from a plurality of items of current value information on the basis of the pressure that is detected by the pressure sensor. The control section is configured to set a current value of a current that is output to the electromagnetic proportional valve on the basis of the current value information that is selected. The current value information expresses a correspondence relationship between a current value of a current that is input to the electromagnetic proportional valve and pressure of the second hydraulic fluid that is output from the electromagnetic proportional valve.
A control method according to a third aspect of the present invention is a method for controlling a work implement of a work vehicle. The control method includes steps (a) to (c). Step (a) is acquiring a pressure signal that indicates pressure of a second hydraulic fluid that is supplied from a pilot pressure control valve to an electromagnetic proportional valve. Step (b) is selecting at least one item of current value information from a plurality of items of current value information on the basis of the pressure that is acquired in step (a). Here, the current value information expresses a correspondence relationship between a current value of a current that is output to the electromagnetic proportional valve and pressure of the second hydraulic fluid that is output from the electromagnetic proportional valve. Step (c) is setting the current value of the current that is output to the electromagnetic proportional valve on the basis of the current value information that is selected in step (b).
It is preferable that the control method further include steps (d) to (f). Step (d) is controlling the electromagnetic proportional valve by outputting the current value that is set in step (c) to the electromagnetic proportional valve. Step (e) is applying a pilot pressure to a switching valve using the second hydraulic fluid that is output from the electromagnetic proportional valve that is controlled in step (d). Step (f) is switching a supply direction of a first hydraulic fluid that is supplied to the work implement on the basis of the pilot pressure that is applied in step (e).
According to the present invention, it is possible to appropriately automatically control a work implement.